Lubricant compositions

ABSTRACT

A LUBRICANT COMPOSITION ESPECIALLY USEFUL IN DIESEL ENGINES CONTAINING A MAJOR AMOUNT OF A LUBRICATING OIL, AN AMOUNT OF A SALT OF A DIVALENT METAL AND AN ALKYLSALICYLIC ACID, AS DISPERSANT, EFFECTIVE TO DISPERSE DEPOSIT FORMING MATERIALS IN THE OIL MEDIUM, AND A VISCOSITY IMPROVING AMOUNT OF A HYDROGENATED RANDOM COPOLYMER OF BUTADIENE AND STYRENE CONTAINING SUBSTANTIALLY ONLY AROMATIC UNSATURATION.

United States Patent O m US. Cl. 252-39 11 Claims ABSTRACT OF THE DISCLOSURE A lubricant composition especially useful in diesel engines containing a major amount of a lubricating oil, an amount of a salt of a divalent metal and an alkylsalicylic acid, as dispersant, effective to disperse deposit forming materials in the oil medium, and a viscosity improving amount of a hydrogenated random copolymer of butadiene and styrene containing substantially only aromatic unsaturation.

BACKGROUND OF THE INVENTION In modern high speed diesel engines great demands are made on the lubricating oil used with relation to dispersant properties and viscosity properties.

The dispersant properties of the lubricating oil must be on a high'level in order to insure that the inside of engine cylinders remains clean and that deposition of carbonaceous products on pistons and in piston grooves is counteracted, so that piston sticking is prevented.

With respect to their viscosity properties lubricating oils for internal combustion engines are classified according to a design introduced by the American Society of Automotive Engineers. According to this designated SAE classification such lubricating oils are categorized in two groups on the basis of their viscosity at --18 C. and 99 C., respectively. These groups are the wintergrades and.

normal grades. Each of the two groups is divided into a number of classes. The classes of the winter grades are indicated with the letter W preceded by a number, e.g. a 5W, W or W oil. The winter grades have a specified maximum viscosity at l8 C. The classes of the normal grades are indicated by a number only, viz. a 20, 30, 40 or 50 oil. The normal grades must have a viscosity at 99 C. within a specified range. Generally, oils complying to a certain winter grade do not comply with the viscosity requirement for any normal grade as well, and, conversely, oils complying to a certain normal grade do not comply with the viscosity requirement for a winter grade. Lubricating oils that fall within one SAE class only (viz. either comply with a normal or a winter grade) are designated as single-grade lubricating oils. Examples of widely used single-grade lubricating oils are SAE-ZO- and SAE- oils. On the other hand, lubricating oils which do in fact comply with the specification of both a winter grade and a normal grade are designated as multigrade lubricating oils. Examples of multigrade lubricating oils are the 5W/20, 5W/30, 10W/ 30, 10W/40, 10W/50, 20W/40, 20W/50, 10W/20 and 20W/30 oils.

The viscosity properties of lubricating oils can also be expressed in the form of the viscosity index, which is a relationship between the viscosities of the lubricating oil at 100 F. and at 210 F. A high viscosity index which indicates a relatively small difference between the viscosity of the oil at the temperatures mentioned, is desirable since it facilitates cold starting and precludes the oil from becoming too thin-flowing (and consequently losing its lubricating action) at high temperatures.

' From the foregoing it will be clear that multigrade oils, which must have a relatively low viscosity at low tem- Patented Sept. 25, 1973 per-atures and a relatively high viscosity at high temperatures must have a high viscosity index. The addition to a lubricating oil of designated viscosity index improvers, in order to increase the viscosity index of the oil and thus to make it possible to prepare a multigrade lubricating oil, is known. In general viscosity index improvers are polymeric substances.

Compounds which can act as a dispersant in lubricating oils are known. Up till now, however, the addition of a viscosity index improver to an oil containing a compound with a dispersant action, resulted in a serious decrease of the cleanliness performance of that oil in diesel engines, compared with the cleanliness performance of the same oil without a viscosity index improver.

SUMMARY OF THE INVENTION It has now been found that a combination of a certain type of compounds with a dispersant action and a certain type of viscosity index improvers exists, which when added to lubricating oil renders to that oil cleanliness properties in diesel engines comparable to those of the same oil containing the compound with dispersant properties only.

According to the invention there is provided a lubricant composition comprising a major amount of a lubricating oil, an amount effective to disperse deposit-forming materials in said oil of a salt of a divalent metal and an alkylsalicylic acid wherein the alkyl group contains from 12 to 30 carbon atoms, and a viscosity improving amount of a hydrogenated random copolymer of butadiene and styrene containing substantially only aromatic unsaturation.

For the purposes of this invention a copolymer of butadiene and styrene is understood to be a copolymer which does not contain units derived from conjugated diolefins other than butadiene, and which does not contain units derived from vinyl aromatic monomers other than styrene.

DESCRIPTION OF PREFERRED EMBODIMENTS The alkylsalicylic acid suitable for use in the composition of this invention contains an alkyl substituent having from 12 to 30 carbon atoms and preferably from 14 to 18 carbon atoms.

The salt of a divalent metal and an alkylsalicylic acid preferably is a zinc salt or a salt of an alkaline earth metal, such as magnesium, calcium, strontium or barium. The calcium salts of alkylsalicylic acids are especially preferred.

During the combustion process inside the engine the sulfur compounds present in the engine fuel may form sulfur trioxide (S0 which is converted into sulfuric acid with the water present in the combustion gases. Since this sulfuric acid may induce corrosion of metal parts of the engine, it is desirable that a neutralizing agent be present in the lubricating oil. It has been found that this desire can be satisfied by employing the salts of a divalent metal and an alkylsalicylic acid in the form of basic salts. By the term a basic salt of a divalent metal and an alkylsalicylic acid as used in the description of this invention is meant a compound of a divalent metal or a mixture of compounds of divalent metals which contains, besides the divalent metal, also one or more acid radicals of alkylsalicylic acids and wherein the number of gram equivalents of divalent metal is greater than the number of gram equivalents of alkylsalicylic acid. The basicity of such salts of divalent metals can be expressed in the formula where M stands for the number of equivalents of divalent metal and Z for the number of equivalents of alkylsalicylic acid, for example per 100 grams of the basic metal salt. Such salts can be prepared by methods well known in the art such as described in British Pat. 790,471 or 818,323. A basicity of the divalent metal salts up to about 300% is in general amply sufficient for the above purpose. The use of basic salts with a basicity between 50 and 250% is preferred.

Alkylsalicylic acids can conveniently be prepared by carboxylating alkylphenols. The alkylphenols concerned can be obtained by alkylation of phenols (such as phenol or cresol) with an olefin of 12 to 30 carbon atoms or a mixture of olefins such as a technical mixture of olefins with 14 to 18 carbon atoms, in the presence of acid catalysts, e.g. acid activated clays. The alkylphenols prepared may be converted into the corresponding alkylsalicylic acids by the techniques known for this conversion from the literature. A convenient procedure is, for instance, as follows. The alkylphenols are converted with the aid of an alcoholic caustic solution into the corresponding alkylphenates and the latter are treated with CO at about 140 C. and a pressure of 10 to 30 atmospheres. From the alkylsalicylates so obtained the alkylsalicylic acids may be liberated with the aid of, for example, 30% sulfuric acid.

Neutral and basic salts of divalent metals may likewise be prepared from these alkylsalicylic acids by the methods described in the literature for this conversion. For the preparation of neutral calcium salts the alkylsalicylic acids may, for instance, be converted into the corresponding sodium salts and these may be allowed to react with an equivalent amount of CaCl For the preparation of basic calcium salts with a relatively low basicity, for instance 50%, the alkylsalicylic acids may be treated with 2 equivalents of calcium in the form of Ca(OH) For the preparation of basic calcium salts with a high basicity, for instance 200%, the alkylsalicylic acids may be treated with 4 equivalents of calcium in the form of Ca(OH) with introduction of 1.6 equivalents of C The hydrogenated copolymers of butadiene and styrene useful in the composition of the invention consist of hydrogenated random copolymers of butadiene and styrene, either linear or coupled as known in the art. The copolymerization can be carried out according to known techniques, e.g., in emulsion. It is preferred, however, to carry out the random copolymerization in solution with an alkyl-alkalimetal compound (e.g., a lithium alkyl) as a catalyst in the presence of a randomizing agent such as an ether or a tertiary amine. For example, a mixture of butadiene and styrene can be polymerized in solution using butyllithium as a catalyst and tetrahydrofuran as a randomizing agent. Polylithio initiators may also be used.

The percentages of the number of units derived from styrene and of units derived from butadiene in the random copolymer may vary between wide limits, but preferably the percentage of the number of units derived from styrene lies between and 60, in particular between 30 and 55%, calculated on the total number of units derived from butadiene and styrene together. Most preferred are random copolymers of butadiene and styrene containing between 61 and 45% of units derived from butadiene and between 39 and 55% of units derived from styrene.

The hydrogenation can be carried out in any desired way with any convenient hydrogenation catalyst; for instance, copper or molybdenum compounds. Catalysts containing noble metals or noble-metal compounds can very suitably be used as hydrogenation catalysts. Preferred are catalysts containing a non-noble metal or a compound of Group VIII of the Periodic Table, viz. iron, cobalt and in particular nickel. As examples may be mentioned Raney nickel and nickel on kieselghur. Especially preferred are hydrogenation catalysts which are obtained by causing to react metal hydrocarbyl compounds with organic compounds of any one of the Group VIII metals, iron, cobalt or nickel, the latter compounds containing at least one organic radical which is attached to the metal atom by means of an oxygen atom, for instance as described in British Pat. 1,030,306. Particularly preferred are hydrogenation catalysts obtained by causing to react an aluminium trialkyl (e.g., aluminium triethyl, and in particular aluminium triisobutyl) with a nickel salt of an organic acid (e.g., nickel diisopropylsalicylate, nickel naphthenate, nickel Z-ethyl-hexanoate, nickel di-tert-butylbenzoate, nickel salts of saturated monocarboxylic acids obtained by reaction of olefins having from 4 to 20 carbon atoms in the molecular with carbon monoxide and water in the presence of acid catalysts), or with a nickel. enolate or phenolate (e.g., nickel acetonyl-acetonate, the nickel salt of butyrylacetophenone). The hydrogenation of the copolymer is suitably carried out in solution in a solvent which is inert during the hydrogenation reaction. Saturated hydrocarbons, such as butanes, pentanes and cyclohexanes, are very suitable.

The hydrogenation may be carried out to the extent of providing a random copolymer of butadiene and styrene containing substantially only aromatic unsaturation. It is preferred that the hydrogenation is carried out to such an extent that'more than preferably all, of the olefinic double bonds in the copolymer originating from the butadiene are hydrogenated, while no more than 5% of the aromatic rings are hydrogenated.

The molecular weight of the hydrogenated random copolymer of butadiene and styrene is suitably from 20,000 to 200,000, in particular from 25,000 to 75,000.

The amount of the salt of a divalent metal and an alkylsalicylic acid to be present in the lubricant compositions of the invention may vary between wide limits. In general the amount of divalent metal in the form of a salt of an alkylsalicylic acid is between 0.01 and 10% by weight, the preferred amount being between 0.1 and 4% by weight.

The amount of the hydrogenated random copolymer of butadiene and styrene to be present in the lubricant compositions of the invention may vary between wide limits and may depend on the viscosity of the lubricating oil to be used and on the viscosity index of the lubricant composition desired. In general amounts of said hydrogenated copolymer between 0.5 and 5% by weight are very suitable.

The lubricating oil to be used in the lubricant compositions of the invention may be a synthetic or a fatty oil, but preferably is a mineral lubricating oil. The 0115 can be paraffinic, naphthenic or aromatic in nature, or be mixtures of the types mentioned. Paraffinic types of lubricating oils, which can be obtained by solvent extraction of distillate and/or residual fractions of mineral oils are very suitable, since therewith lubricating oil compositions with a high viscosity index can be prepared.

In addition the lubricant compositions of the invention may contain other additives such as antioxidants, foam inhibitors, anti-corrosion agents, such as zinc (11- alkyl dithiophosphates, agents to improve the lubricating action, detergents such as polyisobutenyl-polyethylenepolyamines and polyisobutenylsuccinimides of tetraethylenepentarnine, and other substances which are usually added to lubricating oils.

Although the lubricant compositions of the invention are highly suited to be used in diesel engines, they can also be used in gasoline engines, or in any other device wherein the use of lubricant compositions with a high viscosity index is appropriate.

EXAMPLE I In a paraflinic lubricating oil, originating from a Middle East crude, were dissolved 6.5% w. of a calcium salt of an alkylsalicylic acid (the alkyl substituents containing 14-18 carbon atoms) with a basicity of 200%, 2% w. of a commercial polyisobutenylsuccinimide of tetraethylenepentamine (Lubrizol 894) and 0.4% of a commercial zinc dialkyldithiophosphate (Lubrizol 1395). In the lubricating oil composition so obtained several viscosity index improvers were dissolved in such amounts that a 20W/40 oil was obtained. These viscosity index improvers consisted of a hydrogenated random copolymer (according to the invention) of butadiene and styrene with a molecular weight of about 55,000 and containing a ratio of units derived from butadiene to units derived from styrene of 57 to 43, of which the olefinic double bonds were hydrogenated for more than 95% and the aromatic rings for less than 5% (in composition A); as viscosity improvers not according to the invention a commercial polyalkyl methacrylate (Plexol W 1500) (in composition B), and a copolymer of long-chain alkyl methacrylates and hydroxyethyl methacrylate (in composition C) were used. Also for comparative reasons a composition D was prepared, which differed from composition A in that the calcium salt of alkylsalicylic acid Was replaced by 2.3% w. of a calcium petroleum sulfonate (Santolube 291). The compositions A and D contained equal amounts of calcium.

The lubricant compositions were tested in a Gardner 112 single cylinder diesel engine that was run for 32 hours under constant conditions at a moderately high speed and load, with constant fuel supply. The temperature of the upper ring groove was maintained at 290 C. As can be seen from Table I, which shows the results, use of the compositions B and C not according to the invention gives rise to a serious decrease in piston cleanliness as compared with the piston cleanliness obtained with the lubricating oil without viscosity index improver, while the use of composition A according to the invention substantially does not change the piston cleanliness. Composition D gave a very low piston cleanliness rating. Due to heavy blow-by and loss of load this test (Run 5) had to be terminated after hours running. All rings were completely stuck.

The hydrogenated random copolymer of butadiene and styrene described in Example I was also tested in a more severe engine test, namely, a modified Caterpiller 16 engine test. The test conditions were those of the Caterpillar 16 test, except that a fuel conaining 1% of sulfur was used, and no oil change was carried out. The test duration was 240 hours. In the 20W/40 parafiinic oil, originating from a Middle East crude, tested, were present, besides the hydrogenated copolymer described in Example I (1.5% w.), 10.5% w. of a calcium salt of an alkylsalicylic acid (the alkyl groups containing 14-18 carbon atoms) with a basicity of 200%, 4% w. of a commercial polyisobutenylsuccinimide of a polyethylene poly amine (Oronite 1200) and 3.4% w. of a commercial zinc di(octylphenyl)dithiophasphate (Oronite 260)-designated composition E. For comparison the same oil without the said hydrogenated copolymer (not being a multigrade oil, but a SAE 30 oil) and the same oil wherein the hydrogenated copolymer was replaced by 6.6% w. of a commercial polyalkyl methacrylate (Plexol W 1500), designated composition F, were also tested. Table H shows, that the composition E according to the invention substantially does not change the cleanliness performance,

while the oil consisting of composition F has a lower cleanliness performance.

1 Maximum=70. 9 Maximum-=10.

We claim as our invention:

1. A lubricant composition comprising a major amount of a lubricating oil, an amount eifective to disperse deposit-forming materials in said oil of a basic salt of a divalent metal in which the metal is zinc or an alkaline earth metal and an alkylsalicylic acid in which the alkyl substituent has from 12 to 30 carbon atoms, said salt having a basicity of 50-300% and a viscosity improving amount of a hydrogenated random copolymer of butadiene and styrene containing substantially only aromatic unsaturation and having a molecular weight of from 20,000 to 200,000.

2. A lubricant composition according to claim 1 wherein said alkyl substituent has from 14 to 18 carbon atoms.

3. A lubricant composition according to claim 2 wherein the divalent metal is calcium.

4. A lubricant composition according to claim 1 wherein the basicity of the basic salt is between 50 and 250%.

5. A lubricant composition according to claim 1 wherein the number of units derived from styrene in the random copolymer is between 5 and 60%, calculated on the total number of units derived from butadiene and styrene together.

6. A lubricant composition according to claim 5 wherein said percentage is between 39 and 55% 7. A lubricant composition according to claim 1 wherein the molecular weight of the hydrogenated random c0- polymer of butadiene and styrene is from 25,000 to 75,000.

8. A lubricant composition according to claim 1 wherein in the hydrogenated random copolymer of butadiene and styrene over of the olefinic unsaturation is reguced and up to 5% of the aromatic unsaturation is reneed.

9. A lubricant composition according to claim 1 wherein the amount of divalent metal in the form of a salt of an alkylsalicylic acid is between 0.01 and 10% by weight.

10. A lubricant composition according to claim 1 wherein the amount of the hydrogenated copolymer of butadiene and styrene is between 0.5 and 5% by weight.

11. A lubricant composition according to claim 1 wherein the lubricating oil is a mineral lubricating oil.

References Cited UNITED STATES PATENTS 2,223,129 11/ 1940 Prutton 252-39 X 3,625,893 12/1971 Brook et a1. 252-39 X 2,798,853 7/ 1957 Young et al 252-59 X 2,293,419 8/1942 Van Ess 252-39 X FOREIGN PATENTS 522,959 3/1956 Canada 25239 1,146,925 3/1969 Great Britain 25239 HELEN M. S. SNEED, Primary Examiner 

